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So a few weeks back, I mentioned tearing down the throttle body I replaced in my 2012 Cruze due to getting the nice P2135 that many members have had. One thing that I noticed was that I was only getting it during cold morning starts and I never had an issue with it while driving. This lead me to believe there was a noisy potentiometer somewhere in the system that was being impacted by temperature. I decided to make this post simply to outline how the Cruze Drive-By-Wire throttle body works. One thing that motivated me was that a member here stated that there was a “resistive film” inside the throttle body that wears down after use. This is simply untrue! The throttle body is nothing more than a housing, motor, and 2 slide pots.


Here we have on the bench the suspect throttle body:



First thing I did was remove the blade by removing the 2 T20 screws holding it to the shaft. The blade only slides out 1 way due to the 2 bumps on it blocking movement in the other direction.





Next, was to remove the electronics from the housing, I removed the 5 clips holding the plastic casing to the throttle body housing, this was done simply with a flat head screwdriver.




I assumed that the assembly just pop right out then, but it turns out I was wrong. It turns out that I needed to brake off the “cap” that his been epoxied to the the top of the plastic housing to reveal the potentiometer







You can see the wiper that connects to the circuit board in the white plastic part. Unfortunately I destroyed it while removing it from the shaft:



These 4 “fingers” are connected in pairs and are used to make contact on the circuit board, just like a standard slide potentiometer. I was unable to easily remove the metal portion which held the wiper as it was pressed on so I destroyed that and was able to remove the circuit board and plastic housing from the assembly.





What you see here is the inner mechanical workings. It contains a motor, a reduction gear and the gearing to the shaft inside the housing. The shaft also has a clockspring on it so that the throttle blade will return to the closed position when the motor is not engaged:




I turned my focus to the electronics now. By forcing the wiper off the shaft, I scratched up the PCB a bit, but I still can see how it works


these are the four tracks to the potentiometer:



this is the connection to the motor:




Basically, the 6 pin connector connects through the plastic housing to the following:


Pin 1: Motor
Pin 2: Motor
Pin 3: Wiper
Pin 4: Wiper
Pin 5: Wiper
Pin 6: Wiper


Likely what happens is they PWM the voltage going to the motor depending upon pedal press and that allows the motor to get to a position then they hold it at that position.


Pins 3-6 is where all your issues likely are. The motor on this device works fluidly with no issues, you can see right here when I apply 5V to the motor leads it turns no problems:


http://i767.photobucket.com/albums/xx318/meltingplastic/CruzeTB/VID_20150406_175009844.mp4


Looking at the potentiometer portion, I measured 1.8k at both pots. Pins 3 and 6 are connected via the wiper to the top slider. Pins 4 and 5 are connected via the bottom slider. I'm assuming that GM provides 5V to pin3, GND to Pin 4 and they measure they somehow jump the remaining 2 pins and monitor the voltage created. As the motor turns the shaft, the wiper will move, creating a change in voltage between 0V and 5V. Looking at the PCB, I can see that potentiometer had begun to wear down even only after 50k miles, especially on the top track. This would provide the wrong reading to the ECM for where the PWM value is commanding the motor to turn the shaft to (usually has a built in tolerance) and then the computer throws the code.


Looking at the PCB, my PCB was built on week 40 of 2011 (the 4011). It was built by PREH which appears to do a lot of automotive electronics according to their website (Preh GmbH). Now i'm pretty sure that the PCB part number is 13070-147. I tried to desolder the PCB the connections to the housing are coated and I didnt feel like trying to remove it as I'm pretty sure it was have gained me no new knowledge.


After tearing this thing down, the only way to repair a “bad” throttle body would be as follows:



  1. Determine a way to easily remove and reinstall a new wiper arm
  2. Desolder and resolder a new PCB as this is the failure point
  3. Reattach the cap with some sort of epoxy to prevent any water/debris from contacting the board.

Because the wiper arm is pressed on, this is likely the reason why there is no quick “fix it” kit for this. Maybe a kit would include a new machined shaft for the blade which would allow for the wiper arm to be screwed on somehow after replacing the PCB.


Hopefully you guys find this informative. Let me know if you have any questions or maybe even access to the wiring schematics so I can understand what signals are applied to pins 3-6, though I know 2 are going to be 5V and GND.
 

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One thing that motivated me was that a member here stated that there was a “resistive film” inside the throttle body that wears down after use. This is simply untrue! .....

Looking at the PCB, I can see that potentiometer had begun to wear down even only after 50k miles, especially on the top track. This would provide the wrong reading to the ECM for where the PWM value is commanding the motor to turn the shaft to (usually has a built in tolerance) and then the computer throws the code.
First off, nice work! That's what I like about this place. You guys are figuring this all out well before I have a problem. It saves me all the trouble. :)

But it looks to me you just proved that member's statement. What am I missing?
 

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Discussion Starter · #4 ·
But it looks to me you just proved that member's statement. What am I missing?
I may have taken their post wrong (and I'm too lazy to dig around for it) but I read it as if there was a film inside the housing by the blade that wears down, not part of a potentiometer. I could be wrong but I remember reading it a few times and being like what are they talking about?
 

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I may have taken their post wrong (and I'm too lazy to dig around for it) but I read it as if there was a film inside the housing by the blade that wears down, not part of a potentiometer. I could be wrong but I remember reading it a few times and being like what are they talking about?
I may not have read their post, but my reaction is they were referring to the film that makes up the potentiometer. Bottom line, things rub. That restive stuff can only take so much. That's just how they work. There is such a thing as a step potentiometer - a series of contacts with resistors between them. So the stuff that rubs is metal on metal. It can take a lot more wear, but the response is "stepped". The other is to go with some kind of optical encoder method.

But for us end users, all we can do is not tap our right foot to the beat of the music. :grin:
 
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Unfortunately, it seems more and more things are designed to be disposable, not serviceable.
To some extent, it may be due to liability as much as anything else. The courts will probably hold the designer partly responsible if some dumb mechanic assembles it wrong and has a accident. By selling it as a complete unit and assembled in the plant, they avoid a lot of that. It's designed to wear out at that point and fail gracefully before anything weird can happen to the motor or other parts of the throttle.

Granted, it's all speculation, but I'm sure legal liability is in the minds of the engineering department.
 
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Discussion Starter · #8 ·
To some extent, it may be due to liability as much as anything else. The courts will probably hold the designer partly responsible if some dumb mechanic assembles it wrong and has a accident. By selling it as a complete unit and assembled in the plant, they avoid a lot of that. It's designed to wear out at that point and fail gracefully before anything weird can happen to the motor or other parts of the throttle.

Granted, it's all speculation, but I'm sure legal liability is in the minds of the engineering department.
More than likely, but it's only an amount of time until dorman or some other company comes out with the a new replacement. Truthfully $100 isn't TOO bad for a new one, as long as you have the ability to remove the 4 bolts then reinstall them but some people aren't confident enough to do it on their own anyway. Though, for someone looking to spruce up their engine bay, it would be nice to be able to remove the electronics assembly, powder coat the housing, then reinstall everything.
 
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